In recent years, a capsule endoscope having an imaging function and a radio communication function appears in a field of endoscope. After being swallowed by a patient, i.e., a subject (human body), from the mouth for an observation (examination), the capsule endoscope travels through inside internal organs (body cavities) such as esophagus, stomach, and small intestine following peristaltic movements and sequentially captures images using the imaging function until naturally discharged from a living body of the subject, in other word, during an observation period.
During the observation period in which the capsule endoscope travels through the internal organs, the capsule endoscope captures images in the body cavities thereby obtaining image data, and sequentially transmits the image data to an outside of the subject using the radio communication function, i.e., by radio communication. Then, the image data is accumulated in a memory inside a receiving apparatus provided outside the subject. When the subject carries the receiving apparatus equipped with the radio communication function and the memory function, the subject can move freely without inconveniences even after swallowing the capsule endoscope and before discharging the same, i.e., even during the observation period. After the observation finishes, a doctor can display images inside the body cavities on a display unit or the like based on the image data accumulated in the memory of the receiving apparatus, and make diagnosis (see Patent Document 1, for example).
There are various types of capsules corresponding to areas whose images are to be captured, for example, there are capsules for esophagus, stomach, small intestine, and the like. The capsule starts imaging after reaching a relevant organ. Further, some capsules that travel through body cavities following the peristaltic motions measure pH, temperature, and the like in the body cavity, and transmit measurement data to the receiving apparatus outside.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-19111